Allow SSO Group lists longer than 255 characters

[hardillb]

fixes #6102

Description

This allows for unlimited SSO groups list length rather than limiting to 255 characters

Related Issue(s)

#6102

Checklist

• I have read the contribution guidelines
• Suitable unit/system level tests have been added and they pass
• Documentation has been updated
  • Upgrade instructions
  • Configuration details
  • Concepts
• Changes flowforge.yml?
  • Issue/PR raised on FlowFuse/helm to update ConfigMap Template
  • Issue/PR raised on FlowFuse/CloudProject to update values for Staging/Production
• Link to Changelog Entry PR, or note why one is not needed.

Labels

• Includes a DB migration? -> add the area:migration label

[codecov]

Codecov Report

❌ Patch coverage is 60.71429% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 76.80%. Comparing base (4d412ea) to head (1c75fb2).
⚠️ Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
forge/ee/routes/sso/auth.js	0.00%	7 Missing ⚠️
...ge/db/migrations/20251006-01-fix-sso-group-type.js	80.95%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6103      +/-   ##
==========================================
- Coverage   76.81%   76.80%   -0.01%     
==========================================
  Files         380      381       +1     
  Lines       19230    19253      +23     
  Branches     4624     4627       +3     
==========================================
+ Hits        14771    14788      +17     
- Misses       4459     4465       +6     

Flag	Coverage Δ
backend	76.80% <60.71%> (-0.01%)	⬇️

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[knolleary]

Approved, pending two minor comment updates to clarify the migration for future reference

[knolleary]

Revoked my approval as I thought the DB migration filename needed updating - I was wrong. Still approved.